Storm and/or security shutters and doors have been manufactured in a roll-up format for many years. They commonly roll up and down onto and from a take-up reel above (or below or to the sides of) the protected opening using a mechanism that turns the take-up reel and/or drives the material of the shutter directly. The material of the shutter curtain covering the protected opening is generally flat, comprising a large number of (usually identical, typically extruded metal) slats. Unique top slats may be used to interface to the take-up mechanism, and unique bottom slats may be used to seal or cushion against the surface upon which the curtain rests. Adjacent slats interlock, making a curtain whose structural strength, wind, and impact resistance is derived from the basic strength of the slats themselves.
The curtain is lowered into and rides in tracks on the sides. The tracks hold the slats in the form of a planar curtain, provide a guide for deployment, and anchor the curtain to the fixed structure surrounding the protected opening. The curtain is limited in width because the slats must accept wind loads and impacts, especially those normal to the plane of the curtain, without flexing sufficiently to touch (and break) windows, doors, etc. in the protected opening. The curtain must also resist flexing that may pull the curtain from within the tracks. As the curtain is widened to protect larger openings, it is necessary to reinforce the curtain against flexure normal to the curtain plane using storm bars (running vertically in most cases) or to break the curtain into several narrower spans, each riding between reinforcing bars or in its own set of (usually vertical) parallel edge tracks. In either case, when the curtain is retracted, the protected opening remains obstructed by the reinforcing bars or the additional tracks.